The subject invention generally relates to methods of synthesizing a double metal cyanide (DMC) catalyst.
Polyether polyols are integral intermediate components utilized to manufacture a wide array of products, including polyurethanes. As such, the production of polyether polyols is critical. It is known in the art that polyether polyols are produced from the polymerization of epoxides, such as propylene oxide (PO) and ethylene oxide (EO). It is also known in the art that double metal cyanide (DMC) catalysts are effective catalysts for the polymerization of the epoxides. DMC catalysts produce polyether polyols having narrow molecular weight distributions as well as relatively low unsaturation.
In conventional methods, DMC catalysts are prepared by combining an aqueous solution of a metal salt and an aqueous solution of a complex metal cyanide salt. As a specific example, an aqueous solution of ZnCl2 (excess), as the metal salt, is combined with an aqueous solution of K3Co(CN)6, as the complex metal cyanide salt. This combination precipitates out the desired DMC catalyst, in this case specifically Zn3[Co(CN)6]2. Examples of such conventional methods are disclosed in U.S. Pat. Nos. 5,470,813 and 5,714,639. These conventional methods, in one form or another, utilize a complex metal cyanide salt. The complex metal cyanide salts are very expensive which limits the economic viability of utilizing DMC catalysts in the production of polyether polyols. One reason these complex metal cyanide salts are so expensive is that they are pre-purified. That is, any secondary products, such as KCl, which may have the potential of wholly or partially deactivating the DMC catalysts, are removed from the complex metal cyanide salt before the ZnCl2 is combined with the complex metal cyanide salt.
Thus, it would be desirable to provide methods of synthesizing DMC catalysts that do not utilize expensive complex metal cyanide salts as intermediates thereby improving the economic viability of DMC catalysts utilized in the production of polyether polyols.
The present invention provides various methods of synthesizing a double metal cyanide (DMC) catalyst. As disclosed above, the methods of the subject invention do not utilize complex metal cyanide salts to synthesize the DMC catalyst.
The method of the subject invention, in a single step, combines an aqueous solution of a first metal salt of the general formula M(X)n wherein M is selected from the group consisting of aluminum, zinc, and the transition metals; X is an anion selected from the group consisting of halides, hydroxides, sulfates, acetates, carbonates, cyanides, oxalates, thiocyanates, isocyanates, isothiocyanates, carboxylates, and nitrates; and n is a value from 1 to 3 satisfying the valency state of M with an aqueous solution of a second metal salt of the general formula N(Y)n wherein N is selected from the group consisting of the transition metals and the lanthanides; Y is an anion selected from the group consisting of halides, hydroxides, sulfates, carbonates, cyanides, oxalates, thiocyanates, isocyanates, isothiocyanates, carboxylates, and nitrates; and n is a value from 1 to 3 satisfying the valency state of N; and with an aqueous solution of an alkali metal cyanide to form a suspension having a particle phase and a continuous phase. The particle phase comprises the DMC catalyst synthesized from the combination of the aqueous solutions of the first metal salt, the second metal salt, and the alkali metal cyanide. The continuous phase comprises a secondary product such as KCl. In this method, the DMC catalyst is produced independent of a complex metal cyanide salt.
In an alternative method of synthesizing the DMC catalyst, the aqueous solution of the first metal salt and the aqueous solution of the second metal salt are each independently fed into the aqueous solution of the alkali metal cyanide. In a further alternative method of synthesizing the DMC catalyst, the aqueous solution of the metal salt of the general formula N(Y)n, i.e., the second metal salt, is combined with the aqueous solution of the alkali metal cyanide of the general formula XCN to form an intermediate solution comprising a DMC catalyst precursor and the secondary product. In this method, the aqueous solution of the metal salt of the general formula M(X)n, i.e., the first metal salt, is next combined with the intermediate solution such that the DMC catalyst is synthesized upon reaction between the DMC catalyst precursor and the first metal salt. In either alternative method, the DMC catalyst is produced independent of a complex metal cyanide salt.
Various methods of synthesizing a double metal cyanide (DMC) catalyst are disclosed. More specifically, the methods of the subject invention synthesize the DMC catalyst by combining aqueous solutions of a first metal salt, a second metal salt, and an alkali metal cyanide in different manners.
An aqueous solution of the first metal salt is prepared. The strength of the aqueous solution of the first metal salt can range from 1 to 50 parts by weight of the first metal salt based on 100 parts by weight of the aqueous solution. Similarly, aqueous solutions of a second metal salt and an alkali metal cyanide are also prepared. The strengths of these aqueous solutions can also range from 1 to 50 parts by weight of the second metal salt and the alkali metal cyanide, respectively, based on 100 parts by weight of the aqueous solution. In any event, it is most preferred that the first metal salt is combined in molar excess relative to the second metal salt. In other words, the molar ratio of the first metal salt to the second metal salt is greater than 1. This molar ratio preferably ranges from 1.1:1 to 6:1, more preferably from 1.1:1 to 3:1.
Additionally, at least one of the aqueous solutions of the first metal salt, the second metal salt, and the alkali metal cyanide further comprise a water-soluble, organic activator. As understood by those skilled in the art, organic activators activate the surface of the DMC catalyst to improve the overall activity of the catalyst. If included, the water-soluble, organic activator preferably comprises at least one of ethanol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, isobutyl alcohol, and glyme. Other water-soluble, organic activators are known in the art. The most preferred organic activator for purposes of the subject invention is tert-butyl alcohol. If included, the water-soluble, organic activator is preferably introduced in a washing step as described below.
The first metal salt of the subject invention observes the general formula M(X)n. In this formula, it is to be understood that M is selected from the group consisting of aluminum, zinc, and the transition metals, X is an anion selected from the group consisting of halides, hydroxides, sulfates, acetates, carbonates, cyanides, oxalates, thiocyanates, isocyanates, isothiocyanates, carboxylates, and nitrates, and n is a value from 1 to 3 satisfying the valency state of M. In preferred embodiments of the subject invention, M is selected from the group consisting of Al(III) and Zn(II), X is selected from the group consisting of halides and acetates, and n is a value from 1 to 3 satisfying the valency state of M. The first metal salt of the subject invention may comprise at least one of zinc acetate and aluminum acetate. Most preferably, however, the first metal salt of the subject invention is ZnCl2.
The second metal salt of the subject invention observes the general formula N(Y)n. In this formula, it is to be understood that N is selected from the group consisting of the transition metals and the lanthanides, Y is an anion selected from the group consisting of halides, hydroxides, sulfates, carbonates, cyanides, oxalates, thiocyanates, isocyanates, isothiocyanates, carboxylates, and nitrates, and n is a value from 1 to 3 satisfying the valency state of N. In preferred embodiments of the subject invention, N is selected from the group consisting of the Fe(II), Fe(III), Co(II), Co(III), Nd(III), Y is selected from the group consisting of halides, and n is a value from 1 to 3 satisfying the valency state of N. The second metal salt may comprise neodymium chloride. However, it is most preferred that the second metal salt is CoCl2.
It is to be understood that Group IA alkali metals may be utilized for the alkali metal cyanide of the subject invention. Preferably, the alkali metal cyanide utilized is KCN. However, it is to be understood that other alkali metal cyanides, such as LiCN and NaCN, may be utilized without varying the scope of the subject invention.
In one embodiment, all three aqueous solutions can be combined in a single step. That is, the aqueous solutions of M(X)n, N(Y)n, and the alkali metal cyanide can be combined, in independent feed streams, into a reaction vessel, which is originally empty. As will be understood from that described below, the methods for synthesizing the DMC catalyst according to the subject invention are flexible, i.e., robust, and the order of addition or the time of addition (e.g. simultaneous or separate) is not critical.
In another embodiment, the method of the subject invention first combines the aqueous solution of M(X)n and the aqueous solution of N(Y)n to establish a first aqueous solution. The first aqueous solution may, for example, be formed in a pre-mix vessel. The first aqueous solution, including the aqueous solutions of both the first metal salt, M(X)n, and the second metal salt, N(Y)n, is then combined with the aqueous solution of the alkali metal cyanide, such as an aqueous solution of KCN, to form a combination product, i.e., the DMC catalyst.
The first aqueous solution, preferably from the pre-mix vessel, may be combined with the aqueous solution of the alkali metal cyanide in different manners. For instance, the aqueous solution of the alkali metal cyanide may be prepared in the reaction vessel, and the first aqueous solution from the pre-mix vessel may be added to the reaction vessel. Alternatively, the aqueous solution of the alkali metal cyanide may be added to the first aqueous solution in the pre-mix vessel. Alternatively, the reaction vessel may initially be empty, and the first aqueous solution and the aqueous solution of the alkali metal cyanide may be combined, or added, into the reaction vessel at the same time but via separate feed streams.
In yet another embodiment, the aqueous solution of the first metal salt and the aqueous solution of the second metal salt are each independently fed into the aqueous solution of the alkali metal cyanide in a single step to synthesize the DMC catalyst. That is, in this embodiment, the aqueous solution of the alkali metal cyanide is in the reaction vessel, and the aqueous solutions of the first and second metal salts are not first combined. Instead, each of these aqueous solutions remains separate, i.e., not pre-mixed, and they are independently fed into the aqueous solution of the alkali metal cyanide.
In yet another method of the subject invention, the aqueous solution of the metal salt of the general formula N(Y)n, i.e., the second metal salt, is combined with an aqueous solution of the alkali metal cyanide. As understood by those skilled in the art, the alkali metal cyanide has the general formula XCN, wherein X is selected from the group consisting of alkali metals. For example, an aqueous solution of CoCl2 is combined with an aqueous solution of KCN. The combination of the aqueous solution of the second metal salt with the aqueous solution of the alkali metal cyanide forms an intermediate solution. This intermediate solution comprises a DMC catalyst precursor and a secondary product. The secondary product is of the general formula XnY, wherein n is a value from 1 to 3 that satisfies the valency state of Y.
In the example set forth immediately above, the DMC catalyst precursor is a complex comprising at least cobalt atoms, originally from the CoCl2, and cyanide (CN) anion, originally from the KCN, and the secondary product comprises KCl. In addition, it is also possible that the DMC catalyst precursor comprise potassium (K) ion.
It is to be understood that the secondary product is intended to describe any compound that, in any way, wholly or partially deactivates the DMC catalyst. Therefore, as understood by those skilled in the art, it is preferred, but not necessary, to substantially eliminate the secondary product from the combination product of the aqueous solutions of the first metal salt, the second metal salt, and the alkali metal cyanide such that the DMC catalyst is not deactivated.
Next, an aqueous solution of a metal salt of the general formula M(X)n, i.e., the first metal salt, is combined with the intermediate solution formed as described above such that the DMC catalyst is synthesized upon reaction between the DMC catalyst precursor and the first metal salt.
In any of the embodiments described above, the combination of all of the aqueous solutions forms a suspension having a particle phase and a continuous phase. The particle phase comprises the DMC catalyst synthesized from the combination of the aqueous solutions of the first metal salt, the second metal salt, and the alkali metal cyanide, and the continuous phase comprises the secondary product.
For the purpose of eliminating the secondary product and isolating the DMC catalyst, the particle phase is separated from the continuous phase. Separating the particle phase from the continuous phase helps to ensure that the DMC catalyst is not deactivated in any way by the secondary product. Separating the particle phase from the continuous phase can be accomplished by various techniques. Once the particle phase is separated from the continuous phase, the particle phase can be washed with the water-soluble, organic activator.
One such technique is to filter the suspension to collect the particle phase, which comprises the DMC catalyst, as a retentate or residual product. After the particle phase is collected as the retentate, the retentate is preferably dried. The preferred manner in which to dry the retentate is by air-drying. However, in any of the embodiments described herein various forms of heat may be used to dry the retentate. In this technique, although not necessary, the retentate may be triturated or washed with the water-soluble, organic activator prior to drying. In other words, the suspension can be filtered and then dried, without triturating or washing, or the suspension can be filtered, triturated or washed, and then dried. As understood by those skilled in the art trituration is essentially a washing step that also incorporates some form of agitation, such as mixing, and washing does not typically incorporate any form of agitation.
Another technique for separating the particle phase from the continuous phase is to hold the suspension until the continuous phase at least partially separates from the particle phase. In other words, the suspension is held until the particle phase settles to the bottom of the reaction vessel such that the continuous phase is on top of the particle phase. It is preferred to hold the suspension until the continuous phase almost entirely separates from the particle phase. To accomplish this, the suspension is held for from 0.5 to 24, preferably from 1 to 12, hours.
After the suspension has been held, this technique further includes the step of decanting the continuous phase. That is, the continuous phase, which after the holding step is on top, is poured off of or removed from the particle phase. Although not required, this technique may continue by centrifuging the particle phase to separate liquid from the particle phase after the continuous phase has been decanted. As understood by those skilled in the art, the centrifugation step further separates remnants of any liquid from the particle phase. If the particle phase is centrifuged, then the liquid generated in the centrifugation step is decanted. This technique may continue by washing the particle phase with the water-soluble, organic activator after the liquid has been decanted. The different water-soluble, organic activators are as described above with the most preferred being tert-butyl alcohol. Of course, if the particle phase is now washed with the water-soluble, organic activator, then the particle phase is dried after the washing step.
The following examples illustrate the nature of the subject method invention with regard to the methods of synthesizing the DMC catalyst. The examples presented herein are intended to demonstrate the objects of the invention but should not be considered as limitations thereto.